1. Field of the Invention
The present invention relates to an optical information write/read device which writes data in a write verify mode and a writing method therefor.
2. Description of the Prior Art
Recently, optical disks have attracted attention as a high density write/read medium, and they have been developed intensively. An optical disk has remarkable characteristics such as a large storage capacity, non-contact write/read capability and removal of record medium capability. In a prior art write/read device, an optical head writes and reads data with an optical beam in sectors in tracks provided on an optical disk.
However, at present, a so-called write verify is usually needed in order to ensure the reliability of written data by comparing the data read just after the write operation with the original write data or by counting the number of errors or the like detected from error correction signals.
FIG. 1 is an example of a timing chart of a write verify operation of a prior art write/read device. Write data stored in a buffer memory is coded by an error correction circuit, and modulated by a MODEM and written by an optical head in the data fields of each sector of tracks of a side of an optical disk. First, a first piece of data is written in a track "i", and after a revolution (wait) period T of the optical head, the data written in the track "i" is read for verification. The read signal is stored in the buffer memory after demodulation and error detection. If the number of errors is smaller than a prescribed number, the write operation is determined to have been properly performed and writing of the next piece of data is started. The above-mentioned series of write, read and error check is called a write verify, and the write verify of a track of data needs 3 T time periods wherein T denotes a disk revolution time. Following the write verify of the first piece of data, the next piece of data is written in the next track "i+1", and similarly to the data write operation in the track "i", after a rotation, the data written in the track "i+1" is read and checked for write verify. If more than the prescribed number of errors are detected, the data is again written in the same track or alternately written in another good track.
As illustrated in FIG. 1, if the write operation is performed in a write verify mode as explained above, a time period as long as three revolutions (3 T) is needed for the writing of a track. That is, the time period is three times as long as that of a write operation only, and data cannot be written fast.